1. Field of the Invention
The present invention relates to a tuned oscillator for being used as a local oscillator for a tuner of a radio receiver, a television receiver and so on, a sweep oscillator for a spectral analyzer, a microwave measuring instrument and so on.
2. Description of the Prior Art
A tuned oscillator, has previously been proposed such one which uses an YIG (where YIG represents yttrium, iron and garnet but it may contain various kinds of additives) single crystal sphere (as is dislcosed in a published examined Japanese patent application No. 32671/1978). This YIG sphere has various features such as the Q value of resonance characteristic is high in the microwave band; it can be constructed to be small because its resonance frequency is independent on the volume of the YIG; the resonance frequency thereof can be varied linearly over a wide band by changing a biasing magnetic field which applied to the YIG sphere.
However, the above-described tuned oscillator has a defect that due to the YIG sphere used therein, the tuned oscillator is difficult to be integrally formed on an MIC (thin film hybrid microwave integrated circuit) substrate and hence its construction flexibility is restricted. Further, this YIG-tuned oscillator has disadvantages in that the coupling tightness must be matched by adjusting lead wires or ribbons constituting a coupling loop of the YIG sphere and by adjusting the position between the coupling loop and the YIG sphere and that this tuned oscillator is easily affected by vibration.